It depends on what Castore are doing with delivery terms and EU VAT registrations. Part of the problem is the price is inclusive of UK VAT and then you’re potentially paying customs duty on top and VAT in your member state (which is what the DHL charge is).
Pre-Brexit, you wouldn’t have had to pay the customs duty or the local VAT on top, but obviously the rules have changed now we’re out the customs Union.
Basically, Castore need to think about how they’re fulfilling online sale to the EU and pick a member state to register for VAT in, otherwise it’s going to continue costing people a fortune.